How can I create a method in the @implementation of a class without defining it in the @interface?

For example, I have a constructor that does some initialisation and then reads data from a file. I want to factor out the file-reading code into a separate method that I then call from within the constructor. I don't want to define this method in the header because it's private only to this @implementation context.

Is this possible?

Here's my example. I have a little program that read's a Todo task-list from a file.

Here is the @interface:

@interface TDTaskList : NSObject {
NSString* name; // The name of this list.
NSMutableArray* tasks; // The set of tasks in this list.
}
-(id)initListOfName:(NSString*)aName;
-(NSArray*)loadListWithName:(NSString*)aName;
@end

As Andy hinted in the comments, you can use Extensions (which look like a category without a name). The difference is that you must implement the methods declared in an extension whereas the compiler doesn't verify that you implement methods declared in a category.